1. Field of the Invention
The present invention relates to a wireless communication system. More particularly, the present invention relates to a method and an apparatus for controlling uplink transmission power in a wireless communication system.
2. Description of the Related Art
A wireless communication system provides various kinds of communication services, such as voice and data. Generally, a wireless communication system is a multiple access system that can share available system resources (bandwidth, transmission power, etc.) and support communication with multiple users. Examples of the multiple access system include a Code Division Multiple Access (CDMA) system, a Frequency Division Multiple Access (FDMA) system, a Time Division Multiple Access (TDMA) system, an Orthogonal Frequency Division Multiple Access (OFDMA) system, a Single Carrier Frequency Division Multiple Access (SC-FDMA) system, etc.
A wireless communication system needs to control uplink transmission power in order to efficiently use limited radio resources. This is for controlling a size of a reception signal at a base station to an appropriate level. That is, when transmission power is too weak in uplink transmission, the base station cannot receive a transmission signal of a terminal. In contrast, when the transmission power is too strong, a transmission signal of the terminal may act as interference to a transmission signal of a different terminal, and increases battery consumption of the terminal. The wireless communication system controls uplink transmission power to maintain the size of a reception signal at an appropriate level, thereby preventing unnecessary power consumption at a terminal. In addition, the wireless communication system adaptively determines a data transmission rate, etc., thereby improving transmission efficiency.
The uplink transmission power control is roughly classified into an open loop power control and a closed loop power control. The open loop power control measures or estimates signal attenuation of a downlink to estimate signal attenuation of an uplink and compensate for transmission power of the uplink, and determines uplink power with consideration of an amount of radio resources allocated to a relevant terminal or the attribute of transmission data. In the closed loop power control, a base station and a terminal cooperate using feedback information for a transmission power control to control transmission power.
To control transmission power between a base station and a terminal, a Transmit Power Control (TPC) command is used. In the Wideband CDMA (WCDMA) system of the related art, a TPC command is used for both an uplink and a downlink transmission wherein one of a plurality of TPC command values is transmitted. For example, in a 3rd Generation Partnership Project (3GPP) standard, one of four values of −1, 0, +1, +3 dB is transmitted as a TPC command.
Therefore, a need exists for a method and an apparatus for efficiently determining a TPC command for controlling uplink transmission power in a wireless communication system.